The present invention relates to technology for driving control of a brushless motor, and more particularly to technology effectively applied to the formation of rotation drive current waveforms of the motor. The present invention relates to technology effectively applied to a driving control apparatus of a spindle motor for rotationally driving disk type storage media as in, e.g., a hard disk drive.
A hard disk drive is demanded to have the ability to read and write information from and to magnetic disk as fast as possible, that is, the ability to make access at high speed. To achieve this, it is important to speed up disk rotation. Conventionally, a brushless DC multi-phase motor called a spindle motor has been generally used to rotate magnetic disk in a hard disk drive. The magnetic disk is fast rotated by the spindle motor and a magnetic head for read and writing is brought near to the surface of the rotating magnetic disk to write or read information while moving in a radius direction thereof.
In rotation driving control of a conventional spindle motor, a rotor has been rotated by supplying coils of individual phases with square-wave pulse currents as shown in FIG. 15 that are out of phase with one another, by a driving circuit. FIG. 15 shows the waveform of current fed through one of three phases; currents having waveforms that are 120 degrees out of phase with one another are fed through other two phases. Such a rotation driving method based on square-wave pulse currents has the advantage of easy current formation but also the disadvantage of causing rotation variations and noise due to torque ripple. It is known that a brushless motor can be rotated without causing rotation variations and noise by using drive current waveforms of sine waveforms. Accordingly, an invention is proposed which smoothly rotates a rotor by feeding pulse currents of sine waveforms through coils of individual phases (Japanese Published Unexamined Patent Application No. Hei 9(1997)-37584).
However, in the above described technology, plural units of waveform information of one cycle of current waveforms to be formed are stored in ROM (read only memory), depending on the load on the motor, and when a user selectively specifies one of them, the specified waveform information is read out to control coil drive currents, whereby currents of desired sine waveforms are outputted. As a result, the amount of hardware increases, and even if the load on the motor changes, since the duty of basic clock to form coil drive waveforms remains constant, phase switching of output currents cannot be smoothly performed in response to an increase or decrease in the output currents. This fact has been revealed by the present inventors.
An object of the present invention is to provide a magnetic disk unit that can feed currents of sine waveforms through coils by a relatively small-sized circuit, and thereby, enables highly dense magnetic storage with less rotation variations and has a spindle motor rotating at a low noise level.
Another object of the present invention is to provide a magnetic disk unit that can smoothly change output currents in response to changes in the load on a motor, and thereby, enables highly dense magnetic storage with less rotation variations and has a spindle motor rotating at a low noise level.
The above described objects and other objects and characteristics of the present invention will become apparent from the description of this specification and the accompanying drawings.
Typical ones of intentions disclosed by the present patent application will be briefly described below.
A magnetic disk storage apparatus of this invention comprises: a first motor for rotating magnetic disk; a magnetic head for reading information from recording tracks on the magnetic disk; and a first motor driving control circuit for controlling drive currents of the first motor, wherein the first motor is a multi-phase brushless motor in which the potential of a center tap of the multi-phase brushless motor is made to be floating, and a driving control circuit of the first motor performs driving by feedback control so that a coil of one of the phases is driven with a full amplitude at which an applied voltage becomes equal to a source voltage, a coil of a second phase is driven with gradually changing voltages so that a current of sine waveform is delivered, and a third coil is controlled so that a total current flowing through all coils becomes a predetermined current value.
According to the above described means, motor coils can be driven according to sine waveforms without causing power loss, whereby disk rotation variations are reduced, highly dense magnetic storage is enabled, and the motor can rotate at a low noise level.
Preferably, the first motor driving control circuit is provided with an arithmetic circuit that produces by predetermined operations a signal driven with gradually changing voltages so that a current of sine waveform is delivered. Accordingly, in comparison with the method of holding all data corresponding to sine waveforms in memory, a circuit scale can be made smaller and the magnetic disk storage apparatus can be miniaturized.
Moreover, the first motor driving control circuit is constructed to produce as a PWM signal a signal driven with gradually changing voltages so that a current of sine waveform is delivered. A driving method based on the PWM signal enables less power loss than a driving method based on linearly changing currents.
The first motor driving control circuit is constructed to produce as a PWM signal a signal driven with the feedback control. Use of the PWM signal can reduce power loss and enables still less rotation variations because it can be driven with currents corresponding to changing loads.
Moreover, coil currents fed through coils of individual phases by the first motor driving control circuit are formed to have phases that are an predetermined electrical angle corresponding to coil inductance and internal resistance ahead of the phases of back electromotive forces induced in the coils. Accordingly, the motor can be rotated with the greatest driving torque.
Moreover, the first motor driving control circuit drives coils of individual phases so that phase switching timing is off zero-cross points of the back electromotive forces. Thereby, in the case where phase switching control is performed by detecting zero-cross points of back electromotive forces, the detection of incorrect zero-cross points due to noise generated in the coils during phase switching can be prevented, so that highly accurate rotation control can be performed.
The first motor driving control circuit produces signals driven with gradually changing voltages by identical operations even if phases driven by the signals are different from each other so that currents of sine waveforms are delivered. By producing drive control signals of all phases by identical operations, circuit configuration and arithmetic programs can be simplified.
Moreover, in a magnetic disk storage apparatus comprising the first motor driving control circuit and a controller controlling the first motor driving control circuit, the first motor driving control circuit is constructed to perform control so that the total of currents fed through the coils of the phases matches a current indication value supplied from the controller, and a current indication value correcting circuit is provided which corrects the current indication value, taking into account fluctuations of the total current produced by the currents fed through the coils of the phases being changed according to sine waveforms. Accordingly, reaction of the control system to ripples of coil current resulting from driving the motor with a sine waveform can be weakened, with the result that torque ripples can be reduced and rotation variations can be further lessened.